Many products may undergo heat treatment in furnaces for different reasons. For example, in semiconductor wafer fabrication the semiconductor wafers undergo thermal curing, and in steel manufacturing the steel undergoes an annealing process for hardening the steel. Often in semiconductor production the temperature must be controlled very precisely as minor variations in the temperature can affect yields, the temperature may need to be controlled for a specific amount of time and often the temperature needs to be stabilized quickly so that the next step of manufacturing process may begin. Therefore it is imperative that heat treatment can be precisely controlled.
Active fluidic cooling is a well-known method to reduce the cycle time in batch processing furnaces. In this case products will reside within the thermal process chamber and a temperature adjusting medium is forced through the passageways in contact with furnace to adjust the temperature of the thermal process device. Existing systems include a uni-directional flow method, whereby the temperature adjusting medium is injected at one distal end and is exhausted at the other distal end of the thermal process chamber, with this system the distal end where the temperature adjusting medium is injected will cool faster than at the exhaust end due to the transfer of energy, this results in a large sloping temperature gradient across the load which takes substantial time to equalize at the end of the process cycle.
Some improvements have been made by introducing a bi-directional flow, whereby the temperature adjusting medium is introduced alternatingly at both distal ends. In this case the cooling between the two distal ends is more uniform and balanced, however the central mass cools more slowly as some heat capacity is lost as it travels towards the center.
For the batch processing of silicon substrates in a thermal process chamber, new generations of thermal process chambers are being required to support both larger batch sizes and larger size substrates, both resulting in higher masses of material being processed, therefore as the product is treated at high temperatures, e.g. 600-1200° C., more energy is stored in the mass. Therefore with existing cooling systems the cycle time is increased which consequently results in decreased processing capacity.
Accordingly, there is a need to increase the cooling capacity of the thermal processing systems as well as an advantage gained by improving the thermal uniformity during cooling.